This invention pertains to the art of electric interconnect devices and, more particularly, to flexible circuit interconnects.
The invention is particularly applicable to connecting a piezoelectric element or piezo-generator to an electric circuit such as a printed circuit board. However, it will be appreciated by those skilled in the art that the invention could be readily adapted for use with other devices as, for example, where similar flexible circuit interconnects are employed for electrical interconnection.
Piezoelectric elements are typically ceramic devices which produce an electric voltage across the element upon physical deformation. Such elements may be advantageously employed as a piezoelectric transducer in a low tire warning system as is disclosed in U.S. Pat. No. 4,237,728.
Conventional methods for interconnecting a piezoelectric element include use of multiple conventional stamped metal contacts combined with an insulating ring of suitable insulating material. The stamped metal contacts are attached at opposed ends of the piezoelectric element to provide secure interconnections. Typically, the piezoelectric element sits on top of a thin, metallic lower contact with an insulating ring placed adjacent the top portion of the piezoelectric element to insulate the lower contact from an upper contact. The upper contact is then placed over the top of the insulating ring while maintaining an electrically operative connection to a face of the element. The two metallic contacts are extended out beyond the piezoelectric element and connected to the required circuit. In typical applications it is necessary to secure the extended metal contacts with conventional soldering techniques to small diameter pins mounted on a printed circuit board.
An alternate prior art interconnection scheme includes the use of individual insulated hook-up wiring devices soldered to the appropriate contact areas of the piezoelectric element. A special silver-bearing, rosin flux wire soldering material is typically required for this technique.
The various prior art forms and types of circuit interconnects for piezoelectric elements that have heretofore been suggested and employed in the industry have met with varying degrees of success. It has been found that the defects present in most prior interconnects are such that the devices themselves have limited economic and practical value.
The metal contacts scheme in combination with an insulating ring for interconnecting piezoelectric elements has suffered a number of inherent problems. The scheme typically requires use of multiple parts necessitating additional tooling, substantially increased assembly time, and decreased reliabiity resulting from the use of multiple parts. Additionally, the cost of material and installation of the metal contact scheme is undesirable due to the plurality of parts.
The conventional hook-up wire interconnection scheme has suffered from the problems of requiring the use of a special silver-bearing solder and a special soldering technique. The special solder and technique has necessitated hand soldering installation resulting in a time-consuming, inefficient operation that requires considerable skill. The dependence on human technique necessarily encompasses considerable operator error, and ultimately reduced reliability of the interconnection. It has also required considerable inspection and testing procedures for quality control to identify unreliable connections. A particular additional problem of this technique is that the conductor size normally used is in the 0.010" diameter range. Such a small diameter provides little mechanical strength, especially when subject to the normal vibrations that a piezoelectric element experiences during operation. Handling of the device after the soldering operation has also been a particular problem due to the fragile leads.
The present invention contemplates a new and improved device which overcomes all of the above-referred to problems and others to provide a new flexible circuit interconnect for a piezoelectric element which is simple in design, economical to manufacture, readily adaptable to a plurality of uses with piezoelectric elements having a variety of dimensional characteristics, easy to install and which provides improved operational and electrical interconnection.